全文获取类型
收费全文 | 9771篇 |
免费 | 337篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 61篇 |
综合类 | 3篇 |
化学工业 | 1314篇 |
金属工艺 | 93篇 |
机械仪表 | 141篇 |
建筑科学 | 122篇 |
矿业工程 | 7篇 |
能源动力 | 170篇 |
轻工业 | 1393篇 |
水利工程 | 24篇 |
石油天然气 | 31篇 |
无线电 | 180篇 |
一般工业技术 | 619篇 |
冶金工业 | 5417篇 |
原子能技术 | 29篇 |
自动化技术 | 510篇 |
出版年
2023年 | 43篇 |
2022年 | 148篇 |
2021年 | 190篇 |
2020年 | 131篇 |
2019年 | 168篇 |
2018年 | 190篇 |
2017年 | 187篇 |
2016年 | 186篇 |
2015年 | 115篇 |
2014年 | 168篇 |
2013年 | 398篇 |
2012年 | 268篇 |
2011年 | 259篇 |
2010年 | 215篇 |
2009年 | 243篇 |
2008年 | 174篇 |
2007年 | 144篇 |
2006年 | 117篇 |
2005年 | 84篇 |
2004年 | 74篇 |
2003年 | 68篇 |
2002年 | 64篇 |
2001年 | 47篇 |
2000年 | 41篇 |
1999年 | 181篇 |
1998年 | 1608篇 |
1997年 | 918篇 |
1996年 | 640篇 |
1995年 | 379篇 |
1994年 | 333篇 |
1993年 | 353篇 |
1992年 | 75篇 |
1991年 | 120篇 |
1990年 | 87篇 |
1989年 | 118篇 |
1988年 | 113篇 |
1987年 | 108篇 |
1986年 | 101篇 |
1985年 | 65篇 |
1984年 | 30篇 |
1983年 | 37篇 |
1982年 | 46篇 |
1981年 | 53篇 |
1980年 | 71篇 |
1978年 | 56篇 |
1977年 | 165篇 |
1976年 | 369篇 |
1975年 | 43篇 |
1972年 | 33篇 |
1971年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Patients with chlamydial infections (Ct) attending the outpatient Venereal Disease Clinic of Copenhagen from July 1-November 30 1995 were asked to fill in a questionnaire focusing upon knowledge, attitude and behaviour related to sexually transmitted diseases (STDs) in order to strengthen the future prevention of Ct. The questionnaire was answered by 37 men and 35 women with a median age of 27 and 21 years and a median number of three and two sexual partners within the last six months, respectively. Half of the patients had previously had an STD, and 92% had been tested for HIV, of whom one homosexual man was known HIV-positive. Notification about exposure from a partner was the reason for attending for 24%. All but one were in favour of partner notification, but only 6% wanted provider referral. During last intercourse condoms had neither been used with a steady partner by 75% especially by the young and women, who thought themselves safe, nor with a casual partner by 52% especially among the young and men, mainly because of thoughtlessness or perception of low risk. Before the actual STD diagnosis only 49% were able to name one symptom and 35% one complication related to Ct. A majority (79%) stated, that fear of catching another Ct would lead to better protection, and 70% found that more information would have a preventive effect. Future Ct prevention programs in Denmark should include intensified chlamydial screening and partner notification together with centrally produced mass media information supplemented by individual counselling. 相似文献
72.
J. A. H. Coaquira V. A. Chitta N. F. Oliveira Jr. P. H. O. Rappl A. Y. Ueta E. Abramof G. Bauer 《Journal of Superconductivity and Novel Magnetism》2003,16(1):115-118
The transport properties of p-type Pb1?x Eu x Te epitaxial layers were studied as a function of Eu content, temperature, and magnetic field. The low-temperature hole mobility is drastically reduced when the Eu concentration is increased from 0 to 6%, while the hole concentration remains almost constant. A metal-insulator transition was observed for x ≈ 0.04, which is probably induced by the disorder caused by the introduction of Eu. For temperatures down to 10 K, only positive magnetoresistance has been observed at low magnetic fields. An anomalous behavior of the resistivity as a function of temperature has been detected for a Eu content about 5%, which is attributed to the resonance between the localized Eu 4f level and the valence band maximum. 相似文献
73.
74.
Four sets of sweet potato clones obtained by meristem tip culture were used to investigate the effect of feathery mottle virus (FMV) infection on the appearance, sensory quality and chemical composition of the storage roots. This study, encompassing four generations, indicated that FMV infection had a slight effect on carbohydrate metabolism but no effect on the polyphenoloxidase-phenol system. Flavor and texture profile analyses indicated that for one clone, FMV-infected roots were more desirable when baked than healthy roots. Considering the study as a whole, FMV infection did not appear to adversely affect sweet potato sensory properties. Clones produced from the same parent by meristem tip culture might have different compositional and sensory properties. 相似文献
75.
A lectin-like protein was isolated from L. muta venom by gel filtration on BIO Gel P-100 followed by column Chromatography on DEAE-sephades A-50. The protein eluted at 0.4 M Nacl in 0.01 Tris pH 7.3 and exhibited agglutinin activity toward 0+ human erythrocytes. The protein is a dimer with Mr 28 kDa. Amino acid analysis revealed high content of tryptophan and acid recidues and low content of cysteine and methionine residues. No neutral carbohydrates and sialic acid were detected. Circular dichroic spectrum shows 78% of B structure and 1% of alpha structure. In vitro experiments with erythrocytes from rat, rabbit and dog revealed strong agglutination while red blood cells from mice, sheep and goat were not agglutinated. In vivo experiments using anesthetized rats, a sharp and prolonged fall in the blood pressure was observed at protein dose of 1.5 mg/kg. Double dose of protein caused the death of the animal. 相似文献
76.
77.
SA Syed KS Zahir JR Zink O Saglaam RJ Restifo JG Thomson 《Canadian Metallurgical Quarterly》1997,38(4):396-403
Reinstatement and spontaneous recovery of previously extinguished nicotine-taking behavior were examined in rats. Male subjects were trained to self-administer nicotine (30 microg/kg per infusion, IV; one 60-min session per day for 3 weeks). Extinction sessions were then given for 5-10 days during which saline was substituted for nicotine. Subsequently, in the first set of tests for nicotine seeking, the reinstatement of lever presses that previously delivered nicotine was examined after priming injections of saline and nicotine (75, 150 and 300 microg/kg, SC; and 30 and 60 microg/kg, IV). In the second set of tests for nicotine-seeking, rats were tested after an additional 21-day drug-free period during which they were not exposed to the self-administration chambers (a test for the spontaneous recovery of drug seeking), and after priming injections of nicotine (150 and 300 microg/kg, SC). Reinstatement of extinguished food-reinforced behavior after exposure to nicotine was also determined. Priming injections of nicotine reinstated nicotine seeking regardless of the route of administration. In addition, previously extinguished nicotine seeking recovered spontaneously after a 21-day period during which rats were not exposed to the drug-taking environment. Nicotine also reinstated extinguished food-reinforced behavior in rats with a history of nicotine self-administration, but not in drug-naive rats. The present results extend previous work with opioid and stimulant drugs on reinstatement of drug seeking by the self-administered drug. It also appears that, as with other positive reinforcers, the mere passage of time is a sufficient condition for the spontaneous recovery of extinguished nicotine seeking. 相似文献
78.
79.
JR Naranjo B Mellstr?m AM Carrión JJ Lucas NS Foulkes P Sassone-Corsi 《Canadian Metallurgical Quarterly》1997,9(12):2778-2783
Thermal washout curves have been proposed as noninvasive tools for analysing lower airway dimensions and pulmonary blood flow, but how upper airway heat transfer affects these washout curves is unclear. The present study was designed to compare extrathoracic and tracheobronchial contributions to thermal washout curves. Respiratory frequency, air ambient temperature, and body core temperature (tc) were varied in six male subjects before and after immersion in cold (1.1 degrees C) water for up to 2 h under three conditions: 1) control: ambient temperature (tamb) = 25 degrees C, rectal temperature change (delta tre) = 0 degrees C; 2) pre-immersion: tamb = 4 degrees C, delta tre = 0 degrees C; and 3) post-immersion: tamb = 25 degrees C, delta tre = -0.7 degrees C. Both peak expiratory nasal (tpn) and oral (tpo) airstream temperatures were measured. Each subject was tested twice. Expiratory tpo was generally higher than tpn in all conditions. Increasing breathing rates lowered tpn and tpo in the control and cold air environments. Orifice temperatures, which are presumed to reflect upper airway blood temperatures, correlated with both tpn and tpo. Lowering tc had no effect on washout curves during quiet breathing and affected only tpn during rapid breathing. The results suggest that while tracheobronchial conditions may contribute to thermal washout curves, extrathoracic conditions predominate. Strong correlations between orifice temperatures, peak expiratory nasal temperatures and peak expiratory oral temperature demonstrate the dominant role of upper airway heat exchange in determining thermal washout curves. 相似文献
80.